What are the 3 most basic selectors?

<h1>This is an HTML header</h1>

/* Element selector */
h1 {
	color: green;
}

<h1 id="header-1">This is an HTML header</h1>

/* ID selector */
#header-1 {
	color: green;
}

<h1 class="headers">This is an HTML header</h1>

/* Class selector */
.headers {
	color: green;
}